Source : Free On-Line Dictionary of Computing

XHTML
     
         A reformulation of
        {HTML} 4.01 in {XML}.  Being XML means that XHTML can be
        viewed, edited, and validated with standard XML tools.  At the
        same time, it operates as well as or better than HTML 4 in
        existing HTML 4 conforming user agents.
     
        {Home (http://www.w3.org/TR/xhtml1/)}.
     
        Latest version: 1.0, as of 2000-09-10.
     
        (2000-09-10)